I found it interesting that when I weighed my gear, 1 and 2 L Platy Hoser bladders weighed the same (about an ounce), and that most of the weight (about 3 ounces worth) was in the cap and tubing and such (essentially, this thing: Platy drink tube kit with a camelbak bite valve on it).

So, you do pay a premium in cost and weight for using a bladder. The question is if what you get in return is worth that cost.